The Eagle Nebula Messier 16 (M16) is a conspicuous region of active star
formation, situated in Serpens Cauda. The starforming nebula, a giant cloud of
interstellar gas and dust, has already created a considerable cluster of young
stars. The cluster is also referred to as NGC 6611, the nebula as IC 4703.

The discoverer,
Philippe Loys de Chéseaux,
describes only the cluster when recording his 1745-1746 discovery.
Charles Messier, on his independent
rediscovery of June 3, 1764,
mentions that these stars appeared "enmeshed in a faint glow", probably
suggestions of the nebula. The Herschels apparently didn't perceive the nebula,
so that their catalogs and consequently, the NGC, only describe the cluster.
The nebula was added in the IC II of 1908 as
IC 4703, with "cluster M16 involved", but
the NGC 2000.0 erroneously classifies this object as an open cluster.

The nebula was probably first photographed by
E.E. Barnard in 1895, and by
Isaac Roberts in 1897;
Isaac Robert's finding brought this object into the IC catalog.

Lying some 7,000 light years distant in the constellation Serpens, close to
the borders to Scutum and Sagittarius, and in the next inner
spiral arm of the
Milky Way galaxy from us (the Sagittarius
or Sagittarius-Carina Arm) a great cloud of interstellar gas and
dust has entered a vivid process of star formation.
Open star cluster M16 has formed from this great gaseous and dusty cloud,
the diffuse Eagle Nebula IC 4703, which is now caused to shine by emission
light, excited by the high-energy radiation of its massive hot, young
stars. It is actually still in the process of forming new stars, this
formation taking place near the dark "elephant trunks" which are well
visible in our photograph, as well as in
AAT pictures and
other images of M16.
A deeper insight in the star formation process could be obtained from the
HST images of M16,
published in November 1995;
moreover, they were used for
an animation
simulating the approach to this star forming region, and we provide some
screen sized images (suitable as
backgrounds for your computer screen).

This stellar swarm is only about 5.5 million years old
(according to the Sky Catalog 2000 and Götz) with star
formation still active in the Eagle Nebula; this results in the presence
of very hot young stars of spectral type O6.
The cluster was classified as of Trumpler type II,3,m,n (Götz).
The brightest star of M16 is of visual magnitude 8.24.
At its distance of 7,000 light years, its angular diameter of 7 arc minutes
corresponds to a linear extension of about 15 light years.
The nebula extends much farther out, to a diameter of over 30', corresponding
to a linear size of about 70x55 light years.

Some sources have smaller distances for M16: Kenneth Glyn Jones gives 5,870.
Götz 5,540 light years. Götz states that this is one of the
intrinsically most luminous open clusters, at an absolute magnitude of
-8.21.

M16 is found rather easily, either by locating the star Gamma Scuti, a white
giant star of magnitude 4.70 and spectral type A2 III, e.g. from Altair
(Alpha Aquilae) via Delta and Lambda Aql; M16 is about 2 1/2 deg (19 min in
RA) west of this star. Or, in particular with a pair of binoculars, locate
star cloud M24, and move northward via a pair of
stars of 6th and 7th mag, followed by small open cluster
M18 1deg North of M24, the magnificient Omega Nebula
M17 another 1deg N, and finally another 2deg N, M16.

Star cluster M16 and the Eagle Nebula are best seen with low powers in
telescopes. A 4-inch reveals about 20 stars in an uneven background of
fainter stars and nebulosity; three nebulous concentrations can be glimpsed
under good observing conditions. Under very good conditions, suggestions of
dark obscuring matter can be seen to the north of the cluster.
The Eagle nebula is best seen on photographs, but larger apertures and nebula
filters (O-III) may help to trace some detail visually. The dark pillars can
be seen in large amateur instruments (12-inch up).